This invention relates to firefighting nozzles in which the liquid (usually water) is discharged through a circumferential passage and exits the nozzle in an annular (or "peripheral") jet flow, and more particularly to peripheral jet self-educing nozzles that use a constriction of the liquid channel within the barrel of the nozzle to draw a liquid chemical additive into the stream of liquid to produce a firefighting foam.
Many firefighting nozzles include a baffle at the end. The baffle includes a stem that extends through at least a portion of the barrel of the nozzle and is secured within the barrel by spokes. One popular line of self-educing foam nozzles, sold by Williams Fire & Hazard Control, Inc., utilizes the stem to add foam concentrate to the liquid flow. As described in U.S. Pat. No. 4,640,461, the Williams' nozzle diverts a portion of the stream of water flowing through the barrel of the nozzle into a flow passage within the stem. Foam concentrate is also supplied to the stem through a separate bore that extends through one of the spokes. This arrangement requires that both the stem and at least one of the spokes be wider than otherwise required.
The diverted flow of liquid entrains the concentrate mix within a mixing channel in the stem, and then strikes a deflector plate that is fastened to the downstream end of the baffle. The deflected mixture of liquid and concentrate mix then moves outwardly, and is impacted by another flow of water diverted away from the main flow. As the mixture continues to flow radially outwardly, it finally impacts the main flow as the main flow passes the baffle. Those skilled in the art have believed that the high turbulence provided in this arrangement is desirable for effective mixing of the chemical additives with the liquid flow to produce foam.